Environmental control apparatus for exposure apparatus

ABSTRACT

Disclosed is an environmental control apparatus for controlling a working environment in an exposure apparatus for effecting exposure using exposure light having a wavelength range in which oxygen absorbs the exposure light. The apparatus comprises an ozone removing filter for removing ozone in the air supplied to the exposure apparatus. By use of the environmental control apparatus of the present invention, ozone which is present in the air supplied to the exposure apparatus and absorbs the exposure light can be removed, so that a decrease in the amount of exposure light can be suppressed and hence, the amount of exposure light can be stabilized during exposure.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an environmental controlapparatus for controlling a working environment in an exposureapparatus. More particularly, the present invention is concerned with anenvironmental control apparatus for an exposure apparatus for effectingexposure using exposure light having a wavelength range in which oxygenabsorbs the exposure light.

[0002] In recent years, it has been desired to produce highly integratedsemiconductor circuits. In order to produce such semiconductor circuits,exposure apparatuses have been widely used in which a circuit patternformed on a reticle as a mask is transferred to a photosensitivesubstrate. Hence, there have been increasing demands for an exposureapparatus which is capable of forming an image of high resolution. As atechnique for producing highly integrated semiconductor circuits, therehas been known a technique which utilizes, as exposure light, lighthaving a short wavelength, such as a g-line or i-line light emitted froma mercury lamp, KrF excimer laser light and ArF excimer laser light.Especially, as a technique for producing a DRAM (Dynamic Random AccessMemory) of 1G, a technique which utilizes ArF excimer laser light havinga wavelength as short as 193 nm has been proposed.

[0003] However, when ArF excimer laser light having a wavelength of 193nm is used as exposure light for producing highly integratedsemiconductor circuits, problems arise, such that the amount of exposurelight which reaches the photosensitive substrate decreases and,therefore, becomes unstable during exposure. The causes of theabove-mentioned problems are as follows:

[0004] (1) Light having a short wavelength, such as ArF excimer laserlight of 193 nm, is absorbed by oxygen in an atmosphere. That is, ArFexcimer laser light has a spectral range which includes a specificwavelength range in which oxygen absorbs the ArF excimer laser light.Therefore, in an exposure apparatus in which ArF excimer laser light isused as exposure light, when exposure is effected in a normal atmospherecomprising air having an oxygen content of about 20%, ArF excimer laserlight is absorbed by oxygen during exposure. Therefore, the amount ofexposure light which reaches the photosensitive substrate decreasesduring exposure.

[0005] (2) When oxygen absorbs ArF excimer laser light, ozone isproduced. Since ozone also absorbs ArF excimer laser light, the amountof exposure light which reaches the photosensitive substrateprogressively decreases and therefore becomes unstable during exposure,leading to difficulty in monitoring the amount of exposure light forwhich highly precise measurements are required.

[0006] Accordingly, it is presumed that the above-mentioned problemsaccompanying a technique which utilizes exposure light having a shortwavelength can be obviated by removing oxygen in an area including alight path in an exposure apparatus in a manner such that the area ispurged with an inert gas and sealed, or an inert gas is continuouslysupplied to the area for removing oxygen.

[0007] However, when the removal of oxygen in an area including a lightpath is conducted in such a manner as mentioned above, there are variousdisadvantages as follows:

[0008] (1) When an area including a light path is completely sealed, itis difficult to load and unload a mask and a photosensitive substrate inthe light path.

[0009] (2) When an area including a light path is adapted to be sealableusing a gate for loading and unloading a mask and a substrate, which isprovided in a carrying means for the mask and substrate, it is difficultto periodically perform maintenance for a substrate stage.

[0010] (3) A sealing structure which has a large internal volume and isvery complicated is required, due to a large degree of motion of asubstrate stage.

[0011] (4) It is difficult to form a sealing structure having asufficient pressure resistance against a difference in pressure betweenthe interior and exterior thereof.

[0012] (5) When light is transmitted through a sealing structure havinga large internal volume, the temperature distribution in the sealingstructure becomes non-uniform, so that it is difficult to control thetemperature of the sealing structure.

SUMMARY OF THE INVENTION

[0013] In view of the above circumstances, a primary object of thepresent invention is to provide an environmental control apparatus foruse in an exposure apparatus for effecting exposure using exposure lighthaving a wavelength range in which oxygen absorbs the exposure light,which has a simple construction and which suppresses a decrease in theamount of exposure light, so that the amount of exposure light can bestabilized during exposure.

[0014] According to the present invention, there is provided anenvironmental control apparatus for controlling a working environment inan exposure apparatus for effecting exposure using exposure light havinga wavelength range in which oxygen absorbs the exposure light, whichcomprises an ozone removing filter for removing ozone in the airsupplied to the exposure apparatus.

[0015] According to one preferred embodiment of the present invention,the environmental control apparatus further comprises an airconditioning system having an air circulation passage for supplying airhaving a controlled temperature to the exposure apparatus and the ozoneremoving filter is disposed in the air circulation passage of the airconditioning system.

[0016] According to another preferred embodiment of the presentinvention, the environmental control apparatus further comprises ozoneconcentration detection sensors which are disposed upstream anddownstream of the ozone removing filter in a flowing direction of theair supplied to the exposure apparatus, and a device for detecting adegree of clogging of the ozone removing filter on the basis of outputsfrom the ozone concentration detection sensors.

[0017] When the environmental control apparatus of the present inventionwhich comprises an ozone removing filter is used for an exposureapparatus for effecting exposure using exposure light having awavelength range in which oxygen absorbs the exposure light, undesirableozone which is produced from oxygen and absorbs the exposure light canbe removed by the ozone removing filter. Therefore, the environmentalcontrol apparatus of the present invention is advantageous in that adecrease in the amount of exposure light can be suppressed and,therefore, the amount of exposure light can be stabilized duringexposure. By use of the environmental control apparatus of the presentinvention, it has become unnecessary to form in the exposure apparatus asealing structure for sealing an area including a light path. Therefore,the above-mentioned disadvantages accompanying a technique whichutilizes a sealing structure (such as difficulties in loading andunloading a mask and a photosensitive substrate, performing maintenance,controlling a temperature of the sealing structure and the like) can beobviated. Although oxygen is relatively stable in a normal atmosphereand difficult to remove using a filter, ozone created by exposure lightis relatively unstable in the same atmosphere and is highly reactive, sothat it can be readily removed using a filter.

[0018] Since ozone has an adverse effect on a photoresist on thephotosensitive substrate, the environmental control apparatus of thepresent invention is also advantageous in that an adverse effect on thephotoresist due to ozone can be suppressed.

BRIEF DESCRIPTION OF THE DRAWING

[0019]FIG. 1 is a schematic illustration showing a system comprising anexposure apparatus which utilizes a preferred embodiment of theenvironmental control apparatus according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] Hereinbelow, an embodiment of the present invention is describedin detail, with reference to FIG. 1. In this embodiment, theenvironmental control apparatus of the present invention is employed fora projection exposure apparatus for producing semiconductor integratedcircuits.

[0021]FIG. 1 is a schematic illustration showing a projection exposureapparatus system which utilizes a preferred embodiment of theenvironmental control apparatus according to the present invention. Thesystem generally comprises a projection exposure apparatus 10, an airconditioning system 12 having an air circulation passage for controllinga working environment in the projection exposure apparatus 10 and acontrol system 14. The projection exposure apparatus 10 comprises alight source 16 for emitting exposure light, such as ArF excimer laserlight; a reticle 22 having a predetermined pattern formed thereon (notshown); an illumination optical system 18 for transmitting the exposurelight emitted from the light source 16 to the reticle 22; a mirror 20for guiding the transmitted exposure light from the optical system 18 tothe reticle 22; a reticle stage 24 for receiving and shifting thereticle 22; a projection optical system 26 for projecting to a wafer 28an image of the predetermined pattern (not shown) formed on the reticle22; a wafer stage 30 for receiving and shifting the wafer 28; and awafer loader 32 for loading the wafer 28 onto the wafer stage 30. Thelight source 16 is not limited to that for emitting ArF excimer laser.Any light sources can be employed, as long as they emit exposure lighthaving a wavelength range in which oxygen absorbs the exposure light.

[0022] As shown in FIG. 1, in the projection exposure apparatus 10, ArFexcimer laser light as exposure light is emitted from the light source16 and controlled by the illumination optical system 18 so as to have apredetermined illuminance range and a predetermined illuminancedistribution. The resultant exposure light is transmitted to the reticle22 having a predetermined pattern. The exposure light passes through thereticle 22 and reaches the wafer 28 on the wafer stage 30 through theprojection optical system 26, to thereby form an image of thepredetermined pattern of the reticle 22 on the wafer 28. The wafer 28 isshifted in the X and Y directions by the wafer stage 30. (The left andright direction in FIG. 1 is defined as the “X” direction, and thevertical direction relative to the plane of FIG. 1 is defined as the “Y”direction.) By the motion of the wafer 28, an image of the predeterminedpattern of the reticle 22 can be transferred to a predetermined portionof the wafer 28. After completion of exposure of the wafer 28, theexposed wafer 28 is removed for replacement from the wafer stage 30 bythe wafer loader 30.

[0023] The air conditioning system 12 is adapted to effect airconditioning around the wafer stage 30 in the projection exposureapparatus 10. The air circulation passage of the air conditioning system12 is substantially blocked from the outside. In the air conditioningsystem 12, air is introduced from an air supply opening 36. Aftercontrolling the flow rate of air by an air damper 38, the air flowsthrough a chemical filter 40, which removes impurities in the air whichhave an adverse effect on exposure. Subsequently, the air passes througha cooler 42 and a heater 44. After controlling the temperature of air bythe cooler 42 and the heater 44, and precisely controlling the flow rateof air to a predetermined value by a fan 46 and a damper 48, the airthen flows through a chemical filter 50, which again removes impuritiesin the air. Then, the air flows through a ULPA filter 52, which removesfine particles in the air, and passes through a wafer stage chamber 53including the wafer stage 30 on which the wafer 28 rests.

[0024] Subsequently, the air flows through a ULPA filter 54 and achemical filter 56, and reaches an ozone removing filter 58 which isdisposed downstream of the wafer stage chamber 53 as viewed in theflowing direction of the air. Ozone is produced during exposure in thewafer stage chamber 53. The ozone is removed by the ozone removingfilter 58. The ozone removing filter 58 comprises materials, typically,such as active carbon, ion-exchange resins, and so on. However, variousmaterials can be employed as long as they adsorb the ozone. The ULPAfilter 54 which is disposed upstream of the ozone removing filter 58 isadvantageously used in the case of the ozone removing filter 58 beingmade of a material which releases fine particles. The chemical filter 56which is also disposed upstream of the ozone removing filter 58 isadvantageously used in the case of the ozone removing filter 58 beingmade of a material which releases a chemical substance having an adverseeffect on exposure. The flow rate of air, after it flows through theozone removing filter 58, is controlled by a fan 60 and a damper 62. Theair is then returned to the cooler 42, so that recirculation of air iseffected.

[0025] Ozone concentration detection sensors 64, 66 are, respectively,disposed upstream and downstream of the ozone removing filter 58 todetect ozone concentrations in the air before and after the air flowsthrough the ozone removing filter 58. The ozone concentration detectionsensors 64, 66 are connected to a control apparatus 68 in the controlsystem 14. The control apparatus 68 detects a degree of clogging of theozone removing filter 58 by making a comparison between outputs from theozone concentration detection sensors 64, 66, to thereby determine atiming of replacement of the ozone removing filter 58. The controlapparatus 68 is connected to a monitor 70. Information supplied from thecontrol apparatus 68, such as a timing of replacement of the ozoneremoving filter 58, is indicated by the monitor 70. The controlapparatus 68 also detects an amount of exposure light, and controls anoutput of the light source 16, based on the detected amount of exposurelight.

[0026] According to the above-mentioned embodiment of the presentinvention, the ozone which absorbs the exposure light can be removed bythe ozone removing filter 58 which is disposed in the air circulationpassage of the air conditioning system. Therefore, a decrease in theamount of exposure light can be effectively suppressed, so that theamount of exposure light can be stabilized during exposure and hence,the amount of exposure light can be precisely detected by the controlapparatus 68. Further, an adverse effect on a photoresist on the wafer28 due to the ozone can be suppressed.

[0027] The present invention has been described above, with reference toone embodiment thereof. However, the present invention is not limited tothe above-mentioned embodiment. Various embodiments are possible withoutdeparting from the scope of the present invention as defined in theappended claims. For example, the environmental control apparatus of thepresent invention can be applied to not only the air circulation systembetween the projection optical system 26 and the wafer 28 as shown inFIG. 1, but also an air circulation system between the illuminationoptical system 18 and the reticle 22, or between the reticle 22 and theprojection optical system 26. Ozone removing filters may be disposed inthe illumination optical system 18 at a site in the vicinity of a mobilereticle blind (not shown) disposed in a conjugate relationship to thereticle 22 and at a site in the vicinity of a revolver (not shown) forcontrolling a stop according to a σ value of the illumination opticalsystem 18.

[0028] The environmental control apparatus of the present invention isadvantageously used when laser light having a relatively broad spectralrange is utilized as exposure light. This is because when a light sourcewhich emits light having a very narrow spectral range is used as thelight source 16, it is possible to select and utilize, as exposurelight, light having a wavelength which is outside the wavelength rangesin which oxygen and ozone absorb the exposure light. However, theenvironmental control apparatus of the present invention may be usedwhen exposure light having a narrow spectral range is utilized. Further,the environmental control apparatus of the present invention isadvantageously used for an exposure apparatus in which higher harmonicsfrom a solid laser or light from a discharge lamp is utilized asexposure light. Additional filters may be used for removing a gas otherthan ozone, if exposure light used has a wavelength range in which thegas absorbs the exposure light.

What is claimed is:
 1. An environmental control apparatus forcontrolling a working environment in an exposure apparatus for effectingexposure using exposure light having a wavelength range in which oxygenabsorbs said exposure light, comprising an ozone removing filter forremoving ozone in the air supplied to said exposure apparatus.
 2. Theenvironmental control apparatus according to claim 1, further comprisingan air conditioning system having an air circulation passage forsupplying air having a controlled temperature to said exposureapparatus, wherein said ozone removing filter is disposed in said aircirculation passage of the air conditioning system.
 3. The environmentalcontrol apparatus according to claim 2, further comprising ozoneconcentration detection sensors which are respectively disposed upstreamand downstream of said ozone removing filter in a flowing direction ofthe air supplied to said exposure apparatus, and a device for detectinga degree of clogging of said ozone removing filter on the basis ofoutputs from said ozone concentration detection sensors.
 4. Theenvironmental control apparatus according to claim 2, wherein saidexposure apparatus comprises a light source for emitting said exposurelight; a reticle having a predetermined pattern formed thereon; anillumination optical system for transmitting said exposure light to saidreticle, to thereby form an image of said predetermined pattern on saidreticle; a projection optical system for transferring said image to awafer; a wafer stage for receiving said wafer; and a wafer stage chamberincluding said wafer stage, and wherein said air circulation passage ofthe air conditioning system runs through an area in said wafer stagechamber between said projection optical system and said wafer stage. 5.The environmental control apparatus according to claim 4, wherein saidozone removing filter is disposed downstream of said wafer stage chamberin the flowing direction of the air supplied to said exposure apparatus.6. The environmental control apparatus according to claim 5, furthercomprising a filter for removing fine particles which is disposedupstream of said ozone removing filter in the air flowing direction. 7.The environmental control apparatus according to claim 6, furthercomprising a chemical filter for removing impurities which is disposedupstream of said ozone removing filter in the air flowing direction. 8.The environmental control apparatus according to claim 7, wherein saidchemical filter is disposed between said ozone removing filter and saidfilter.
 9. An exposure apparatus comprising: a light source for emittingexposure light having a wavelength range in which oxygen absorbs saidexposure light; a wafer stage for receiving a wafer to be exposed tosaid exposure light; and an air conditioning system for supplying airbetween said light source and said wafer stage, said air conditioningsystem including an ozone removing filter for removing ozone in the air.10. An exposure apparatus comprising: a wafer stage for receiving awafer; a light source for emitting exposure light having a wavelengthrange in which oxygen absorbs said exposure light; a reticle having apredetermined pattern formed thereon; an illumination optical system fortransmitting said exposure light to said reticle, to thereby form animage of said predetermined pattern on said reticle; a projectionoptical system for transferring said image to said wafer; a wafer stagechamber including said wafer stage; and an air conditioning system forsupplying air to said wafer stage chamber, said air conditioning systemincluding an ozone removing filter for removing ozone in the air.